1. Field of the Invention
The present invention is directed to a gradient amplifier for use in a magnetic resonance tomography (imaging) apparatus, the gradient amplifier being of the type having at least one control arrangement including a comparator which generates an error signal, and a controller which responds to the error signal to produce a manipulated variable signal, used to operate a gradient coil. The invention is also directed to a magnetic resonance tomography apparatus employing such a gradient amplifier.
2. Description of the Prior Art
Generally, known nuclear magnetic resonance tomography systems have three gradient coils in order to produce linear magnetic field gradients in the x, y and z directions. A precisely controlled current, produced by a gradient amplifier, flows through each of these coils. Each gradient amplifier, for example, sets the current precisely, to within a few mA, in a range between 0 and 300 A. In addition, a rate of rise of the current of about 3.multidot.10.sup.5 A/s is required, for which purpose a voltage of about .+-.300 V must be applied to the coil.
The gradient amplifier contains a current controller for each gradient coil. The characteristics of the controller must be matched to the connected gradient coil. Due to the high precision required, in known tomography systems an expensive calibration by a trained service technician is necessary. For each controller, several potentiometers have to be set by hand. A controller of this sort is known for example from German OS 40 20 213.